This invention relates to methods and apparatus for exchanging frames between bridges to distribute load sharing in a communications network of the kind in which bridges, and related stations and local LANs, e.g. Ethernet LANs and 802 LANs, can be linked by paths in a plurality of sub-networks and wherein the bridges are linked to support a Spanning Tree Protocol (STP) which elects one bridge as a root and then, with respect to said root, computes and utilizes one and only one loop-free set of primary paths between all bridges.
This invention relates particularly to methods and apparatus for examining remaining paths, i.e. paths other than said STP primary paths, between the bridges as possible sub-network paths for a Distributed Load Sharing (DLS) configuration in which frames exchanged between certain stations can utilize more than said STP one set of primary paths between the stations. Certain ones of the remaining paths as are then selected as DLS paths only when certain conditions are met and frames are routed over a selected DLS path only those frames meet certain criteria.
The following document is incorporated by reference in this present application. U.S. Pat. No. 4,706,081 entitled "Method and Apparatus for Bridging Local Area Networks" issued Nov. 10, 1987 to Hart, et al., and assigned to Vitalink Communications Corporation.
The trademark "TransLAN" is registered in the U.S. Patent and Trademark Office and is owned by Vitalink Communications Corporation. This TransLAN trademark is used by Vitalink Communications Corporation on hardward and software for the configurations and methods of the communications system disclosed in the above noted U.S. Pat. No. 4,706,081. The trademark TransLAN is used below in the present application in reference to such hardware and software for the configurations and methods of the communications system disclosed in U.S. Pat. No. 4,706,081.
The Spanning Tree Protocol (STP) computes primary paths between all bridges in a communications network of the kind in which the bridges, and related stations in local LANs, e.g. Ethernet LANs and 802 LANs, can be linked by paths in a plurality of sub-networks.
The spanning Tree Protocol (STP) elects one bridge as a root and then, with respect to said root, computes and utilizes one and only one loop-free set of primary paths between all the bridges.
Some of the remaining paths, i.e. paths other than said STP primary paths between the bridges can, in the STP protocol, be designated as backup paths under certain conditions; but the STP protocol transfers frames only on the primary paths, and not on any of the remaining paths, so long as the primary paths remain effective to function (until some event occurs which requires a re-configuration of the primary paths in the STP protocol).
It is a primary object of the present invention to distribute load sharing in a network in which bridges are linked to support STP by using paths additional to the primary paths for transferring frames between bridges.
It is a related object to distribute load sharing in a way which preserves loop-free paths between all bridges.